Flat commutators with carbon running surface are known in diverse embodiments. In this regard, especially U.S. Pat. No. 5,760,518 A, WO 92/01321 A1, JP 2000208225 A, U.S. Pat. No. 5,637,944 A, EP 667657 A1, U.S. Pat. No. 5,442,849 A, JP 08065967 A, U.S. Pat. No. 6,667,565 B2, EP 1524736 B1, DE 102005028789 A1, JP 11055904 A and DE 102006021696 A1 belong to the pertinent prior art. These known flat commutators with carbon running surface and the methods used for producing them can be subdivided substantially into five groups as follows.
According to a first group of embodiments, a uniform metal part (conductor blank) is overmolded with the plastic that forms the support body. Then the conductor blank is machined down with a lathe on its end face and a annular carbon disk is adhesively bonded or soldered onto the conductor blank, or in other words onto its end face. Then the annular carbon disk is sawed into segments, wherein the conductor blank is also separated into the individual conductor segments insulated from one another. In this production method and the flat commutators produced according thereto, especially the lack of mechanical anchoring of the carbon segments in the support body is a disadvantage, which results in an unsatisfactory—at least for several applications—useful life of the commutator in question. Furthermore, protection of the metal surfaces exposed in the region of the saw cuts is necessary, the production method is laborious and expensive and the consumption of metal material for the conductor segments is very high, which in view of the raw material prices, which have risen considerably in just the most recent times, especially for copper, makes the corresponding flat commutators considerably more expensive.
According to a second group of production methods, an integral metal body, which forms the conductor blank and which in particular may comprise conductor segments joined to one another by means of bridging parts, is soldered or adhesively bonded to a premachined annular carbon disk, so that the two parts form an electrically conductive assembly. Thereafter this assembly is overmolded with plastic in order to form the support body. This is followed by the mechanical machining of the projecting parts (bridging parts) of the metal body and of the terminal hooks for the rotor winding, the surface protection of the metal faces (tinning), the mechanical machining of the frontal carbon surface, the sawing of the annular carbon disk into carbon segments, the bending of the hooks and the machining of the bore. As regards the first group of production methods (see hereinabove), the consumption of metal material is lower here; however, the number of machining operations is similarly high. Nevertheless, the anchoring of the carbon segments in the support body is improved.
In the third group of production methods (see, for example, DE 102005028789 A1), the integral base body is first injection-molded from plastic or is formed in some other way; and then individual metal segments, which already have a finished shape of the hooks and are already surface-protected, are inserted into the support body. Then the inserted conductor segments are joined together with the uniformly premachined annular carbon disk by addition of electrically conductive binder. Then the end face of the annular carbon disk is machined by turning and the disk is sawed to carbon segments and the bore is machined. In this procedure the number of machining operations can indeed be reduced compared with the two groups mentioned first and second; and also the relatively low consumption of metals for production of the conductor segments is advantageous. However, the flat commutators produced in this way are again not adequately reliable, because the carbon segments are poorly anchored.
In the fourth group of production methods, pulverized graphite material is pressed into shape around the conductor blank in order to form the carbon segments (see, for example, JP 08065967 A). Heretofore such a method has proved unsuitable in practice for production of reliable, long-lasting flat commutators with carbon running surface.
In the fifth group of production methods (see, for example, JP 2000208225 and DE 102006021 696 A1) and corresponding flat commutators, typically no metal conductor segments whatsoever are used. In this case, a uniform annular carbon disk is typically overmolded with the plastic of the support body. Then the annular carbon disk is subdivided by saw cuts into the insulated carbon segments. Since it is not possible in such embodiments to wind the rotor winding in the usual manner around the hooks typically disposed on the conductor segments or to weld the hooks, the methods established in this respect for joining the rotor winding to the commutator cannot be employed. Instead, other solutions must be sought, such as using a separate insulating insert, which provides for contacting the ends of the rotor winding directly with the carbon segments, if necessary by using an electrically conductive binder.
Finally, a special approach is taken in JP 11055904 A, according to which individual prefabricated carbon segments are inserted into a support consisting of ceramic and comprising a bottom and a rim, wherein a core likewise consisting of ceramic is inserted in radially inside position between the carbon segments. In this case metal terminal hooks project with an end portion between respectively the radially outside face of a carbon segment and the radially inside face of the support rim. By means of plastic compound, a support body that overlaps the rim of the ceramic support in radially outside position and the ceramic core in radially inside position is then molded onto the unit prefabricated in such a way and comprising ceramic support, ceramic core, carbon segments and terminal hooks. As in many of the methods explained in the foregoing for producing flat commutators provided with a brush running surface formed by carbon segments, the inadequate anchoring of the carbon segments here also does not satisfy the practical requirements and detracts from the useful life.